1. Field of the Invention
This invention relates to a printer control circuit for controlling the operation of various types of printers, such as laser printer, thermal printer, wire-dot printer, and ink-jet printer, and, in particular, to a printer interface circuit embodied in a host system.
2. Description of the Prior Art
FIG. 1 shows a typical prior art system including a host device 1, such as a personal computer, a printer controller 2 and a laser printer 3. When the laser printer 3 is used as an output device, since it cannot be directly connected to the host device 1, there must be provided the printer controller 2 which generally includes a CPU, bit map memory, and a character generator. This is because, the laser printer 3 has its own clock signal for its operation and this clock signal must be synchronized with the supply of print data supplied thereto. Since the host device 1 normally has its own clock signal and the transmission of data to be printed is not in synchronism with the clock signal of the laser printer 3, the laser printer 3 cannot be directly hooked to the host devicel. Thus, the printer controller 2 is provided between the host device 1 and the laser printer 3, whereby the data to be printed is first transferred into the bit map memory of the printer controller 2, from where the data to be printed is transferred to the laser printer 3 in synchronism with the clock signal generated at the laser printer.
The laser printer 3 is very fast in operation and high in resolution and it provides a plain paper output, so that it is desirous to use the laser printer 3 as an output device of various systems, such as personal computers and wordprocessors. However, since the laser printer 3 requires the provision of the printer controller 2 separately, it tends to push up the cost.